1. Field of the Invention
The present invention relates to the measurement of frequency responses of magnetic pickups typically used in musical instruments, and the presentation of the collected data to aid user comparison and selection of magnetic pickups.
2. Description of the Prior Art
Electric guitars and basses (or other applicable instrument in all that follows) use magnetic pickups to capture the vibration of the strings for amplification. These pickups consist of a magnetic core or cores with a winding of wire wrapped around. When ferromagnetic strings vibrate in the magnetic field, a corresponding voltage is induced in the winding. Such pickups have been in common use for decades.
Guitarists in particular are keenly aware that the type and construction of the pickup determines to a large extent the sound that will be produced by a guitar. Guitarists select pickups to obtain a certain sound, and the range of pickup choices in the marketplace runs into the thousands.
However, there are some difficulties related to pickup selection. The first is that they are not inexpensive, sometimes costing a hundred dollars or more apiece, and guitars have typically two or three pickups. This limits the guitarist's selection of pickups to whatever he can afford to physically try in the instrument. If the pickups' sound is unsatisfactory, he is faced with the task of selling them as used pickups at a monetary loss.
It also takes an hour or two to install pickups in an instrument, there being a requirement to remove the strings, disassemble some or all of the instrument, solder in the new pickups, reassemble the instrument, and replace the strings. That makes it difficult to do fast A/B comparisons, and subtle differences between two pickups may not be noticed due to the installation delay.
Pickups also sound different in every guitar, being affected by the type of strings and their age, the shape and construction of the instrument, the type of wood, the ambient temperature and humidity. Other factors contribute as well, such as the acoustic space, and even the player's mental state as he plays. This means that a pickup whose sound is recorded after installation in one instrument will likely sound very different in another instrument, or even in a different room, making pickup comparisons difficult.
Another problem is that pickup tone is described in the trade press and manufacturers' advertisements using inexact language, such as “bright”, “dark”, “woody”, etc., and so trade press pickup reviews are almost useless in pickup selection.
What is needed is a way to quickly compare the sounds of pickups apart from the guitar's acoustic characteristics, and apart from other uncontrollable factors. The measurement and presentation methods described here allow such comparisons, and that is the object of this invention.
Heretofore, there has been no easily usable instrument for measuring the responses of magnetic pickups. One prior art device (Keene) consists of a means for mounting a pickup under a set of guitar strings which are vibrated by an excited coil, with the response being observed using test instruments or the human ear. This arrangement has numerous disadvantages. First, the pickup under test must be removed from any instrument in which it is installed. Second, the range of test frequencies is limited to the vibrational range of the strings and mechanical apparatus, and particularly how they are mechanically excited. (Keene does not suspect that there may be signals or sound sources that are more useful and revealing than vibrating strings.) Third, vibrating strings produce harmonics, some of which are coincident with the fundamental tones of higher pitched strings, confusing the interpretation of the measured data. Fourth, metal strings age and tarnish, making consistent measurements over time impossible. Fifth, the measurement device and system is not portable or easy to use when measuring multiple pickups, and is not usable by groups of musicians distributed worldwide. Most importantly, the measurement arrangement does not provide a way to quickly compare multiple pickups to hear how they sound.
Another method of measuring pickup characteristics involves use of electrical engineering lab equipment. For example, Errede discloses an extensive measurement program for characterizing the electrical parameters of pickups such as inductance, resonant frequency, etc. While this information has technical value and does allow numerical differentiation between pickups, it gives no indication to the human ear how two pickups sound by comparison. Musicians do not understand electronics by and large, and rather need a simple sonic or visual comparison of pickup responses.
Musicians do understand that there are several factors that affect how pickups sound. The construction of the pickup is of course primary. Pickups are generally manufactured in two configurations, single and dual coil. Dual coil pickups were invented to cancel the hum produced by proximity to AC power fields. However, they contain more wire and consequently have more internal resistance and interwinding capacitance, and lower resonant and low-pass roll off frequencies.
Musicians also understand that the resistance of the volume control in the instrument also affects pickup response, as does the capacitance of cables used to connect the instrument to any amplifier.
For example, Gagon, et al. (U.S. Pat. No. 4,545,278, Oct. 8, 1985) states, “The result is that the resistive loading on the pickup is increased (by lowering the load resistance seen by this pickup), which causes the resonance peak to be less high and more wide than that illustrated . . . ” This invention adjusts the resonant peak of the pickup by adjusting the resistive and capacitive load on the pickup. Generally, the lower the resistance, the lower the Q of the pickup's resonance, which of course changes the sound of the pickup. Increasing capacitance decreases the resonant frequency of the pickup, it being primarily inductive. The invention does not disclose how to measure and display such effects so that the guitarist can hear differences between pickups so loaded.
A commercial product, the Stellartone ToneStyler® uses switched resistances and capacitances to change the response of attached passive pickups.
While musicians understand that these factors have an affect on the sound of a pickup, they do not understand exactly how the sound is affected. The present invention and presentation allows the musician to grasp these complex factors neatly and quickly, without theory or mathematics, allowing them to actually hear and see how the sound of the pickup is affected directly.
Allowing the musician to hear how the pickup sounds, apart from an instrument, requires signal processing methods. The notion of placing a sound source into various sonic spaces and replicating frequency responses using digital signal processing and modeling is well established. For example, Kemp (U.S. Pat. No. 7,095,860, Aug. 22, 2006) describes a system for capturing and reproducing the response of a level or frequency control device. The intent there is to simulate real or synthesized responses and process audio as if it originated from a system with such a response. That is, there is an audio source, a processing system, and an output audio signal intended for listener consumption, or later use in recording or the like.
Berson (U.S. Pat. No. 7,184,557, Feb. 27, 2007) describes an invention that “ . . . relates to reproducing stored audio signals in a manner such that the reproduced signals sound as if the stored audio signals had been recorded in a particular acoustic environment.” In fact, there is a well-developed technology base of modeling software and hardware available to musicians that performs just this task. Here again, there is an audio source, a processing system, and an output audio signal.
Ekhaus, et al. (U.S. Pat. No. 6,448,488, Sep. 10, 2002) describes a processing system for musical instrument transducers that can make the instrument sound like a different instrument: “The resynthesized output signal be a microphone output signal, may have acoustic characteristics of another [stringed musical instrument] or possess acoustic characteristics of a “theoretical” [stringed musical instrument].” Here again, there is an audio source (a musical instrument), a processing system, and an output audio signal, possibly sounding like and entirely different musical instrument.
These methods involve creating audio that one might reasonable expect to hear in a certain environment, while in actuality the audio originated in some other environment, or from another instrument of similar type, such as a guitar. The net result and intention of these inventions is presentation of audio to a listener while striving for genuine and believable sound. Even in situations where the implied audio source and environment are not commonly associated, the inventions strive to convince the listener of the reality of the combination. For example, one does not typically hear a symphony in the acoustic space of a concrete stairwell (not the least reason being the physical space required), but the goal of the prior art methods is to get the listener to comment, “That sounds like a symphony orchestra in a stairwell.” The modeling and processing methods do allow new combinations of sources and spaces, but the end product is always the result of processing an audio program source with a certain response, and listening to that result alone.
The present invention has a different goal regarding modeling and aural presentation, that being the comparison of two pickup responses by graphical display and also the playing of audio clips through electronically measured pickup frequency response curves. Typically, a musician has a certain set of pickups in an instrument, and he knows intimately how those pickups sound because he has spent many hours playing that instrument. If he is dissatisfied with the pickups, he will generally know in what direction he desires to change his sound. For example, he might want more high frequency content. Comparing his existing, well-known pickups with others with which he is unfamiliar allows him to quickly determine whether the candidate pickups reflect the change in character that he seeks. In this case, the actual audio clip(s) selected to be processed through pickup frequency responses is not very important, and could be guitar music, but could as well be a prerecorded song, white noise, speech, or any other source having spectral content that illuminates differences between two pickup responses. While the technical methods used to process the audio are similar to prior art methods, the ultimate goal is quite different, that being the rapid comparison of frequency responses. The audio as processed according to the responses need not be ‘believable’, in the sense outlined above, and in fact may not even be related to the music typically reproduced by magnetic pickups.
Musicians are also eager for systems and methods that allow multiple tonalities to be had from one instrument, and as a result inventions exist to accomplish this. For example, Rosendahl (U.S. Pat. No. 5,029,511, Jul. 9, 1991) describes as system for easily exchanging pickups in guitars. This allows the musician to more quickly change pickups and experiment with the sounds that different styles and brands of pickups create. However, the musician must be in physical possession of the pickups so tested, and this is an expensive proposition. And while changing the pickups with such a system is faster than disassembling the instrument, it still takes considerable time as the strings have to be either removed or slackened. Thus it is impossible to do fast A/B comparisons of two pickups. Such systems that allow modular pickup replacement are by far in the minority.